A microfluidic vacuum-pressure-driven device for liquid viscosity measurement

Abstract A vacuum-driven microfluidic viscometer is proposed for measuring dynamic viscosity using only 6 µL of sample. The device consists of a polymethyl methacrylate (PMMA) microchannel with a rectangular cross-section of 200 μm × 450 μm and a total length of 26 cm, connected to a multi-volume micropipette that functions as a controllable vacuum source. Different viscosity levels can be measured without modifying the microchannel geometry by generating different vacuum pressures at the outlet adjusting the pipette volume to 200, 500, or 1000 µL. The measurement principle is based on the linear relationship between fluid viscosity and flow time through the microchannel, as described by Hagen–Poiseuille theory. Viscosity is determined using a time-ratio method with a reference fluid, which reduces the influence of pressure fluctuations and improves measurement stability. Experimental validation with Newtonian fluids over a viscosity range of 0.30–6.18 cP showed good agreement between the device-measured and actual viscosities, with an overall R² value of 0.92. Repeatability analysis showed relative variability ranging from 1.52% to 9.94% across the investigated conditions. Among fluids evaluated at all three pipette-volume conditions, the 500 µL condition produced the lowest percentage measurement errors, ranging from 3.24% to 11.24%. Comparison of the simulation-derived and actual viscosities yielded an overall mean absolute relative deviation of 4.66%. The simple operating principle also supports rapid measurements across multiple vacuum conditions. Owing to its low fabrication cost, small sample requirement, and adjustable vacuum conditions, the proposed micro-viscometer provides a practical and adaptable platform for laboratory and field viscosity measurements.